Method for making a glass to metal seal



May 22, 1962 K. F. MAYERS 3,035,372

METHOD FOR MAKING A GLASS TO METAL SEAL Original Filed March 17, 1951INVENTOR K424 F. Adm 5P5 ATTORNEY United States Patent 3,035,372 METHODFOR MAKING A GLASS T0 METAL SEAL Karl F. Mayers, Somerville, N.J.,assignor to Philips Electronic and Pharmaceutical Industries Corp., acorporation of Delaware Continuation of applications Ser. No. 216,200,Mar. 17,

1951, and Ser. No. 396,218, Dec. 4, 1953. This application Apr. 5, 1957,Ser. No. 651,065

3 Claims. (Cl. 4981) pressure-tight or hermetic seals. The termpressure-tight sea is employed in the specification and claims in ageneric sense to denote a seal which is capable of withstanding pressurewhich may be either equal to or greater than that of the atmosphere.

. A variety of metal-to-glass seals have heretofore been employed inelectrical devices. In one prior type of seal, the metal and glassmembers forming the seal are so selected as to have mean coefiicients ofthermal expansion, that is, thermal coeflicients of linear expansionwhich substantially match over a range of temperatures between thesealing temperature and the ambient or operating temperature of thecompleted seal. The use of metal and glass members having matching meanscoefficients of thermal expansion promotes a strain-free seal. However,such seals are more expensive than is desired for some applicationssince they employ precious metals such as platinum or expensive specialferrous-base alloys including cobalt and nickel. Due to the presentgreatly enlarged demands by the military services, the rare and costlymetal cobalt and also nickel are not as readily available as heretofore.Furthermore, for some applications,

the special'iron-base alloys of the type just mentioned are notparticularly satisfactory since they cannot be machined and worked asreadily as is sometimes desired. Consequently, the metallic portions ofsuch seals are usually made from relatively thin sheet material by aAnother prior metal-to-glass seal employs iron stamp- I ings and ironwire to which are fused a frit or enamel. The bond formed between themetal and the enamel during the manufacture of the seal is weak andtends to leak when the seal is subjected to minor mechanical or is notsatisfactory for most applications.

A further type of seal utilizes a low-expansion glass of theborosilicate type and a tubular copper member having a portion which ismachined or feathered out to a thin edge that is in turn sealed to theglass. Since the copper has a much higher thermal expansioncharacteristic than the glass, the success of the seal depends on theedge portion being'thin enough so that it may stretch and flow underchanges in temperature and pressure. Seals of this type are subject tomechanical failure and are costly to manufacture.

Another seal employs metal and glass members efiectively havingsubstantially matching thermal expansion thermal shock or both.Consequently, :a seal of this I type, although employing a relativelyinexpensive metal,

characteristics, the metal member comprising a core of T 3,035,372Patented May 22, 1962 nickel or iron wire having a relatively heavycopper sheath thereover. The copper sheath is efiective to compensatefor the dilferences in the expansion of the various members.Metal-to-glass seals employing such a sheath are limited to the usetherein of metallic members having very small diameters.

Prior seals of the types mentioned above requiremore or less complexannealing steps, some of which take many hours or days to remove thestresses developed in the glass members of the seals. This annealingoperation further adds to the time of manufacture and the 'cost of thefinished product.

It is an object of the invention, therefore, to provide a new andimproved pressure-tight seal which avoids one or more of theabove-mentioned disadvantages and limitations of prior such seals.

It is another object of the invention to provide a pressure-tight sealwhich is relatively simple in construction and is strong and durable.

It is a further object of the invention to provide a new and improvedmetal-to-glass seal which may be subjected to mechanical and thermalshock without impairing the close adherence of the glass to the metaland the pressure-tight characteristic of the seal.

It is an additional object of the invention to provide a metal-to-glassseal which does not require precious, rare,

or critical metals in the construction thereof.

.It is yet another object of the present invention to prolvide apressure-tight seal which does not require costly a new and improvedmetal-to-glass seal which utilizes in expensive and plentiful metals inthe construction thereof and yet is less subject to mechanical failuresthan are prior metal-to-glass seals.

It is an additional object of the invention to provide new and improvedmethod of making a pressure-tight seal. v

In accordance with a particular form of the invention,

a pressure-tight seal comprises a first metallic member having anaperture therein and having a mean coefiicient of thermal expansion of apredetermined value. The seal further includes a glass insulating membersupported in the aperture in the first member and having a meancoefiicient of thermal expansion substantially lower than that of thefirst metallic member. The pressure-tight seal jadditionally includes asecond metallic member extending through and supported in the glassinsulating member and having arnean coefiicient of thermal expansionsubstantially less than that of the first member and less than that ofthe glassmember. The members mentioned above are relatively sodimensioned that the glass member is restrained under compression by thefirst metallic member in the range of operating temperatures of theseal, contiguous portions of the members being in fused relation.

Further in accordance with the present invention, the method of making apressure-tight seal comprises ,removing the surface contamination from ametallic member having an aperture therein and having a mean coeflicientof thermal expansion of a predetermined value, heating the member in anon-oxidizing and non-reducing atmosphere with glass having a meancoelficient of thermal expansion substantially lower than the aforesaidpredetermined value, to a temperature at which the glass becomes moltenand substantially fills the aperture and fuses to the surface of themetallic member, and then cooling the seal below the melting temperatureof the identified above.

glass, whereby the glass is restrained in the metallic member by strongcompressive forces.

For a better understanding of the present invention, together with otherand further objects thereof, reference is had to the followingdescription taken in connection with the accompanying drawing, and itsscope will be pointed out in the claims.

Referring now to the drawing, FIG. 1 is a bottom perspective view of anelectrical device including a pressure-tight seal in accordance with aparticular form of the invention; FIG. 2 is an enlarged sectional viewof a portion of the device of FIG. 1 taken along the line 2-2 of FIG. 1;and FIG. 3 is a perspective view of a fragmentary portion of anelectrical device including a pressure-tight seal in accordance withanother form of the invention.

Description Seal of FIGS. 1 and 2 Referring now more particularly toFIGS. 1 and 2 of the drawing, there is represented an electrical device10, such as a relay, having a metal cover 11 attached in a suitablemanner as by soldering to a base in the form of a pressure-tight seal12.. Since the latter is pressure tight, the relay may be evacuated ormay just be hermetically sealed to exclude moisture. The seal 12comprises a first metallic member 13 having a plurality of spacedapertures 14, specifically circular apertures, and having a meancoefiicient of thermal expansion of a predetermined value. Although notexpressly limited thereto, the member 13 may be of a standard screwmachine steel often referred to in the trade as B-lll2 or B-11l3 steel.Such steel has a mean coefficient of thermal expansion of approximately140 X 10* units per unit length per degree centigrade. SAE 1010 steelhaving a mean thermal coeflicient of expansion of about 125 X 10-' unitsper unit length per degree centigrade is another suitable material.Other relatively inexpensive and plen- -tiful metals having thermalexpansion characteristics within the range of 110 X 10* to 178 X10 unitsper unit length per degree centigrade may be employed.

Individual glass members of a material such as a lead or lime glass aresupported in individual ones of the apertures 14 in the metallic member13 and each of the members 15 has a centrally disposed aperture 16therein. The pressure-tight seal 12 further includes a second metallicmember 17 supported in each of the apertures 16 in the insulatingmembers 15 and having a mean coeificient of thermal expansionsubstantially lower than the coefficient of the first member 13. Thesecond metallic member 17 may be in the form of a solid cylindricalmetal pin which serves as a terminal for connecting the relay 10 to anexternal electrical circuit. Each of the second metallic members may beof a ferrous-base alloy comprising essentially iron and nickel in theproportions of 40% to 55% nickel and the balance essentially iron, suchan alloy having a mean thermal expansion in the range of 60 X 10* to 97x 10* units per unit length per degree centigrade. A particular exampleof such an alloy found to have utility as one of the second metallicmembers 17 is an iron-nickel alloy containing about 52% nickel and 48%iron.

The glass member 15 has a means coeificient of thermal expansion withinthe range of values of the coefficients for the first and secondmetallic members 13 and 17. Ordinarily the expansion characteristic ofthe glass member 15 is selected so that it is at least equal to orsomewhat greater than that of the metallic member 17.

A glass having a mean thermal expansion coefiicient of about 90 X 10*units per unit length per degree centigrade has proved to seal well withmetals of the type The thermal expansion coefficients of the members 13,15 and 17 are such and the relative dimensions thereof are also suchthat each glass member 15 is restrained in its aperture 14 under radialcompression by the metallic members 13 and 17 in the range of operatingtemperatures of the seal, the interface or contiguous portions of themembers being in fused relation as will be explained more fullyhereinafter.

Method of Making the Seal of FIGS. 1 and 2 It is ordinarily necessary tocondition the metallic members 13 and 17 prior to assembling them infused relation with the glass members 15, to assure a satisfactory bond.It may be desirable to degrease the metallic members in a suitablesolvent such as carbon tetrachloride or trichloroethylene to preparethem for the subsequent film preparation. Alternatively, or followingthe operation just mentioned, the metallic members may be heated orfired in a wet hydrogen atmosphere at a temperature of approximately1000 C. for a relatively short period of time to burn off or remove thesurface contamination or impurities therefrom and to decarbonize thesurfaces thereof. The purpose of a decarbonizing operation is to preventany oxide which may be on the surfaces of the metallic members fromuniting with the carbon to form bubbles in the joint later to be formedbetween the glass and the metal. When the metallic members 13 and 17 areof steel, the surfaces thereof may be oxidized by heating in anoxidizing atmosphere or by dipping the members in a suitable oxidizingsolution such as ferric sulphate and phosphoric acid. A useful solutionhas the proportions of 320 grams of ferric sulphate to 42 centimeters ofphosphoric acid and 6 liters of water. After dipping, the metallicmembers are rinsed in hot, clean water and then preferably driedrapidly. In the next operation the members 13 and 17, regardless of thetype of metal used, are placed in a suitable jig in their propergeometric relation with reference to each other, and the glass is placedin the space between members 13 and 17. The jig, the glass, and themembers 13 and 17 are then introduced into a controlled atmosphere in asealing chamber such as a gas-fired furnace. The burners and the gas andair mixture in the furnace are so adjusted that the atmosphere thereinis effectively neutral, that is, as near as possible nonreducing andnonoxidizing. The elevated temperature of the sealing chamber causes theglass to become molten thereby completely filling the space in theaperture 14 between the members 13 and 17, and the interfaces, or thecontiguous portions of the members, then assume a fused relation orcombination.

The metallic oxide layer on the metallic members may assist in effectinga bond between the glass and the metal because it is soluble in theglass at the fusing temperature and because the oxide layer on themetallic members has an irregular or roughened surface which enhancesthe clinging of the glass to the metal. Next the members are cooledbelow the melting temperature of the insulating or glass member and areremoved from the jigs. Since the thermal expansion characteristics ofthe metallic members 13 and 17 are substantially different and the glass15 has a thermal expansion characteristic within the range of themembers 13 and 17 but at least equal to the inner member 17, theinsulating member is firmly restrained in the aperture 14 underrelatively high radial compression. The member 17 is also firmlyrestrained within the glass member 15. An annealing operation is notemployed thereafter and, in fact, is not desired to relieve any stressesdeveloped in the glass member 15. It is believed that the compressivestresses deliberately developed in the glass member tend to compact thefused joints at the in terface, thereby causing them to be dense andeffecively nonporous and thus effectively preventing leakage which maybe caused by air or gas gradually infiltrating the joints.

The joints thus produced between the glass and the metallic members notonly are nonporous but also are much stronger than conventional jointsand are characterized by their unusal thermal and mechanical resistanceto shock and stress. It has been found that the inner metallic membermay be bent as by careless handling without serious damage to the glassmember or impairing the effectiveness of the seal.

Description of FIG. 3 Seal Referring now to FIG. 3 of the drawing, thereis represented a pressure-tight seal 35 which is similar to thatillustrated in FIG. 1. This seal comprises a first metallic member 31]having a plurality of apertures 31 therein disposed near the peripheryof the member. A glass member 32 is restrained in each of the apertures31 under compression between the first metallic member 31) and a hollowsecond metallic member 33 which forms a terminal pin. The members 31 and33 are in fused relation with the glass members 32. The metallic members30 and 33 have mean coefficients of thermal expansion which aresubstantially different, with member 39 having a substantially highercoefiicient than member 33. The glass member 32 confined between each ofthe metallic members has a mean coefficient of thermal expansion whichis at least equal to that of its associated member 33 but within therange of values of the members 30 and 33. The pressure-tight seal ofFIG. 3 may be made of selected materials as described above and in themanner previously explained in connection with the FIG. 1 embodiment ofthe invention. When a metallic member 30 having, for example, eightapertures 31 is available and only seven thermal pins or members 33 arerequired for some applications, one of the apertures 31 may be sealedwith a solid glass member having no thermal pin therethrough.

FIG. 3 also illustrates the structure which results from a modificationin the method previously described. In lieu of the described oxidizingoperation of steel or ironalloy members 311 and 33, an electrolyticdeposit of a thin film of copper 36 may be made on the surfaces ofmetallic members after surface impurities have been removed therefrom.Thereafter, as explained above, the fusing operation is conducted in thesealing chamber and the sealed assembly is then cooled rather quickly toambient temperature to form the final product, annealing, as beforebeing unnecessary. In this instance, a strong bond between the metallicmembers, the copper film 36 which is integral therewith, and the glassmember 32 is formed which has mechanical and thermal shock resistancecharacteristics similar to the bond between the oxide film and the glasspreviously described. The thin copper film 36 on the metallic membersacts as a cushion between the metallic and the glass members and tendsto relieve stresses in the interface substantially parallel to the axisof a member 33 but not perpendicular to that axis. Manifestly, the glassmember 32 is under relatively high compression due to the describedselection of the metallic and glass members.

From the foregoing descriptions of the various embodiments of theinvention, it will be seen that pressure-tight seal in accordance withthe present invention is relatively simple in construction andinexpensive to manufacture since it utilizes in the construction thereofplentiful and relatively inexpensive materials such as screw machinesteel. It will also be clear that a strong durable bond between themetal and the glass is eflected since the glass is deliberatelymaintained under compression in a manner which tends positively torestrain the glass within the confines of the metal supporting member ormembers. It will also be apparent that since the glass is purposelymaintained under the influence of compressive stresses, time-consumingannealing operations are unnecessary to alleviate those stresses in theglass.

While there have been described What are at present considered to be thepreferred embodiments of this in- 6 vention, it will be obvious to thoseskilled in the art that various changes and modifications may be madetherein without departing from the invention, and it is, therefore,aimed in the following claims to cover all such changes andmodifications as fall within the true spirit and scope of the invention.

What is claimed is:

1. The method of making a compression, hermetic glass-tonnetal sealcomprising the steps of: forming an assembly, in a jig, of an outermetal member having a coefiicient of thermal expansion greater thanapproximately x10 units per unit length per degree centigrade and lessthan approximately 178 10- units per unit length per degree centigrade,said outer metal member having at least one aperture therethrough, atleast one inner metal member within said aperture and spaced from theinner periphery defining said aperture in said outer metal member, saidinner metal member having a substantially lower coefficient of thermalexpansion than that of said outer member, said coeflicient of thermalexpansion of said inner metal member being at least approximately 6()-l()"' units per unit length per degree centigrade but less thanapproximately 97 1O units per unit length per degree centigrade, andglass in the space within said aperture and surrounding said innermember, said glass having a coefficient of thermal expansionsubstantially lower than that of said outer metal member but at leastapproximately as high as that of said inner member and of about 90X 10-units per unit length per degree centigrade; heating the entire assemblyto a temperature at which the glass melts and flows radially of its ownweight to fill the radial space between the inner and outer metalmembers; rapidly cooling the heated assembly from said temperature to alower temperature which is below the annealing temperature of the glassto solidify and to avoid annealing the glass and to set up stresstherein so as to increase the compressive forces holding said glass insaid outer metal member in said glass; and removing said seal from saidjig without annealing said seal.

2. A method as set forth in claim 1 wherein said assembly is heated in asubstantially neutral atmosphere.

3. A method as set forth in claim 1 wherein said surfaces of said outerand inner metal members contiguous with said glass are oxidized prior tosaid assembly with said glass.

References Cited in the file of this patent UNITED STATES PATENTS1,016,320 Burnside Feb. 6, 1912 1,456,110 Mackay May 22, 1923 2,238,599Ramage Apr. 15, 1941 2,279,168 Kalischer et al. Apr. 7, 1942 2,345,278Monack ..,Mar. 28, 1944 2,549,504 Messana Apr. 17, 1951 2,558,878Richardson July 3, 1

FOREIGN PATENTS 475,665 Great Britain Nov. 24, 1937 604,248 GreatBritain June 30, 1948 OTHER REFERENCES Journal of Applied Physics,"volume 17, article beginning on page 685, published in 1946 inLancaster, Pa. by the American Institute of Physics.

Journal of the American Ceramic Society, volume 33, article beginning onpage 224, published in 1950 in Easton, Pa. by the American CeramicSociety.

Glass Industry, volume 27, article beginning on page 389 published in1946 in New York City.

